Abstract:Hadal trenches have been proposed as depocenters of organic material and hot spots for organic matter mineralization. In this study, we for the first time quantified the total benthic O2 uptake in hadal trenches using in situ chamber incubations. Three trenches in the tropical Pacific were targeted and exhibited relatively high diagenetic activity given the great water depths, that is, the Mariana Trench (2.0 × 102 μmol O2 m−2 d−1, 10,853 m), the Mussau Trench (2.7 ± 0.1 × 102 μmol O2 m−2 d−1, 7,011 m), and th… Show more
“…An explanation for a vertical layer ∼ 2000 m in thickness exhibiting anomalously high CH 4 (this study) and 222 Rn (Gamo and Shitashima, 2018) requires sedimentary compounds to be released not only from the axis bottom but also from the trench slopes. Re-suspensions from the trench slope have been commonly suggested by sediment observations that identified the rapid accumulation of the axis sediment, in association with frequent sediment transports from slopes (Nozaki and Ohta, 1993;Glud et al, 2013;Oguri et al, 2013;Luo et al, 2018). As earthquake-induced turbid seawater was indeed evident over the trench slope after earthquake events (Gamo et al, 2007;Kawagucci et al, 2012), this geological force is probably an episodic driver for re-suspension in the IOT.…”
Abstract. Full-depth profiles of hydrographic and geochemical
properties at the Izu–Ogasawara Trench were observed for the first time
using a CTD-CMS (conductivity–temperature–depth profiler with
carousel multiple sampling) system. Additionally, comparative samplings were
done at the northern Mariana Trench using the same methods. A well-mixed
hydrographic structure below 7000 m was observed within the Izu–Ogasawara
Trench. Seawater samples collected from this well-mixed hadal layer
exhibited constant concentrations of nitrate, phosphate, silicate, and
nitrous oxide as well as constant nitrogen and oxygen isotopic compositions
of nitrate and nitrous oxide. These results agree well with previous
observations of the Izu–Ogasawara hadal waters and deep-sea
water surrounding the Izu–Ogasawara Trench. In turn, methane concentrations and
isotopic compositions indicated spatial heterogeneity within the well-mixed
hadal water mass, strongly suggesting a local methane source within the
trench, in addition to the background methane originating from the general
deep-sea bottom water. Sedimentary compound releases, associated with
sediment re-suspensions, are considered to be the most likely mechanism for
generating this significant CH4 anomaly.
“…An explanation for a vertical layer ∼ 2000 m in thickness exhibiting anomalously high CH 4 (this study) and 222 Rn (Gamo and Shitashima, 2018) requires sedimentary compounds to be released not only from the axis bottom but also from the trench slopes. Re-suspensions from the trench slope have been commonly suggested by sediment observations that identified the rapid accumulation of the axis sediment, in association with frequent sediment transports from slopes (Nozaki and Ohta, 1993;Glud et al, 2013;Oguri et al, 2013;Luo et al, 2018). As earthquake-induced turbid seawater was indeed evident over the trench slope after earthquake events (Gamo et al, 2007;Kawagucci et al, 2012), this geological force is probably an episodic driver for re-suspension in the IOT.…”
Abstract. Full-depth profiles of hydrographic and geochemical
properties at the Izu–Ogasawara Trench were observed for the first time
using a CTD-CMS (conductivity–temperature–depth profiler with
carousel multiple sampling) system. Additionally, comparative samplings were
done at the northern Mariana Trench using the same methods. A well-mixed
hydrographic structure below 7000 m was observed within the Izu–Ogasawara
Trench. Seawater samples collected from this well-mixed hadal layer
exhibited constant concentrations of nitrate, phosphate, silicate, and
nitrous oxide as well as constant nitrogen and oxygen isotopic compositions
of nitrate and nitrous oxide. These results agree well with previous
observations of the Izu–Ogasawara hadal waters and deep-sea
water surrounding the Izu–Ogasawara Trench. In turn, methane concentrations and
isotopic compositions indicated spatial heterogeneity within the well-mixed
hadal water mass, strongly suggesting a local methane source within the
trench, in addition to the background methane originating from the general
deep-sea bottom water. Sedimentary compound releases, associated with
sediment re-suspensions, are considered to be the most likely mechanism for
generating this significant CH4 anomaly.
“…Endemic amphipods were collected from the MT (11°N, 142°E), Mussau Trench (MST, 1°N, 149°E), and New Britain Trench (NBT, 6°S, 152–154°E) in early 2017 (Figure and Table ). All three trenches are located in the tropical West Pacific, and the maximum depths of MT (the deepest ocean trench), MST, and NBT are ~11,000, ~7,200, and 9,200 m, respectively (Luo et al, ). Amphipod samples in MT were collected using baited traps during cruise TS‐03 conducted by the Chinese Academy of Sciences in the spring of 2017.…”
The food source of hadal endemic fauna provides an insight into the carbon cycle in trenches and a biological adaptation to the impoverished and harsh trench environment. Here, we present the first Δ14C results of hadal amphipods from three trenches in the Pacific to define the organic matter source in these remote ecosystems. Amphipod muscle tissues contain a bomb 14C signature (Δ14C from 10 ± 2‰ to 65 ± 2‰), thereby revealing a dietary preference for labile and fresh organic matter derived from the surface water. Thus, the carbon cycle in the deepest ocean trench has a tight linkage with the surface ocean via the food chain. The bomb 14C dating result suggests that hadal amphipods have a low tissue turnover rate and an unexpectedly long lifetime (>10 years), at more than 4 times higher than the common longevity (~2 years) of amphipods in shallow waters.
“…However, the hadal zone is not a “biological desert.” Multiple sources of organic matter inputs, combined with special topography and frequent tectonic activities, promote the accumulation of organic matter in the trenches ( Ichino et al, 2015 ; Jamieson, 2015 ; Liu et al, 2018b ). High content of organic matter, abundant microbial cells, and active microbial carbon turnover have been reported in the sediment of multiple trenches, making the hadal trenches “hot spots” of organic carbon degradation in the deep ocean ( Danovaro et al, 2003 ; Glud et al, 2013 ; Wenzhöfer et al, 2016 ; Luo et al, 2018 ).…”
Surprisingly high rates of microbial respiration have recently been reported in hadal trench sediment, yet the potentially active microorganisms and specific microbe–microbe relationships in trench sediment are largely unknown. We investigated the bulk and active prokaryotic communities and co-occurrence interactions of different lineages in vertically sectioned sediment cores taken from the deepest points of the Mariana and Mussau Trenches. Analysis on species novelty revealed for the first time the high rate of novel lineages in the microbial communities of the hadal trenches. Using 95, 97, and 99% similarity as thresholds, averagely 22.29, 32.3, and 64.1% of total OTUs retrieved from sediments of the two trenches were identified as the potentially novel lineages, respectively. The compositions of the potentially active communities, revealed via ribosomal RNA (rRNA), were significantly different from those of bulk communities (rDNA) in all samples from both trenches. The dominant taxa in bulk communities generally accounted for low proportions in the rRNA libraries, signifying that the abundance was not necessarily related to community functions in the hadal sediments. The potentially active communities showed high diversity and composed primarily of heterotrophic lineages, supporting their potential contributions in organic carbon consumption. Network analysis revealed high modularity and non-random co-occurrence of phylogenetically unrelated taxa, indicating highly specified micro-niches and close microbial interactions in the hadal sediments tested. Combined analysis of activity potentials and network keystone scores revealed significance of phyla Chloroflexi and Gemmatimonadetes, as well as several potentially alkane-degrading taxa in maintaining microbial interactions and functions of the trench communities. Overall, our results demonstrate that the hadal trenches harbor diverse, closely interacting, and active microorganisms, despite the extreme environmental conditions.
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